This invention pertains to power conversion in computing systems and other systems which are able to benefit from accurate in-circuit device-resistance data and, more particularly, to a computer system having a power supply in which over-current and/or under-current trip points are adjusted based on FET on-resistance values which are derived while the power supply is actively supplying power to the components of the computer system.
In computer systems today it is common practice to measure the current on each voltage rail. These current measurements are used primarily to sense over-current conditions and other current conditions which require corresponding corrective action.
Sensing the current at the voltage rails typically involves the addition of a high precision resistor to sense the current that is flowing to the load components of the computer system. However, the addition of a precision resistor introduces two problems. First, precision resistors are expensive. Second, the precision resistor must be configured in series with the load in order to measure the current, and the resistor in the series configuration causes an additional undesirable voltage drop which generates undesirable heat in the system and derogates the efficiency of the system.
Some designs, notably certain PWM Controllers, have attempted to improve upon the above described series resistor design by eliminating the series resistor and instead utilizing the inherent resistance of the output device to measure the current. Unfortunately, this method has thus far remained relatively unreliable, imprecise, and inaccurate because the resistance changes with the age and type of output device. Thus, large margins must be designed-in to allow for these fluctuations and changes.